The neuropathology core provides services essential to all four projects. Ad detailed in the projects histopathological changes, whether due to DI vector driven expression of novel genes or analysis of infection in immunodeficient mice, is the critical end point for many of the proposed experiments. Tissue specimens are acquired by the core as part of the experimental procedures. Animals are rarely dedicated solely to acquisition of samples for this core. Exceptions are those procedures (plastic embedding and EM) which require perfusion. Times of tissue acquisition are dictated by the individual experiments and are coordinated by the core director. The core research associate is responsible for processing, sectioning and staining of all tissues. Routine examinations, carried out on the majority of animals include H&E, luxol fast blue of myelin and immunoperoxidase determinations for the distribution of viral Ag. Special stains for specific subtypes of cells, expression of cytokines, in situ hybridizations etc., are dictated by the individual experiments and are also quality controlled and schedule in conjunction with the core director. Epon embedded materials and frozen selections are also processed by the core. We are fortunate to have retained the services of Wen for the past 8 years. He has experience in all of the proposed techniques and has been an invaluable asset to our ongoing research efforts. Depending upon the nature of the experiments, slides are either screened by the core director or read in a blinded fashion by Dr. Hilton or both. Blinded reading of critical experiments eliminates investigator bias. In the past we have published precise protocols for all of the proposed techniques and therefore no difficulties are anticipated. One protocol change worthy of note is the use of the murine mAb designated RIP for staining of oligodendroglia. This mAb is specific for oligodendroglia and recognized oligodendroglia of both rat and mouse origins and can be used on formalin fixed or frozen sections. Supernatants containing the RIP mAb are kindly provided by Regeneron Inc. since they are unable to provide us directly with the hybridoma.